Reductive Activation of C₇₀ Equatorial Carbons and Structurally Characterized C₇₀ δ-Adduct with Closed [5,6]-Ring Fusion

Abstract

The C δ-adducts with closed [5,6]-ring fusion are an important type of compound in classifying bond delocalization in the equatorial belt of C. However, the formation of such compounds is severely restricted due to the low reactivity of the carbon atoms in the flat equatorial region. Such a restriction is lifted when reduced anionic C species are used, where the inert equatorial carbon atoms are activated.

Site-Selectivity of Prato Additions to C70: Experimental and Theoretical Studies of a New Thermodynamic Product at the dd-[5,6]-Junction

“…4 The formation of the dd- [5,6]-adduct was also recently reported for the reaction of α,α′-dibromo-o-xylene to reductively activated C 70 5 and in the reaction with dichlorocarbene. 6 However, there is no report on [5,6]-monoadduct of C 70 by 1,3-dipolar cycloaddition.…”

“…In this study, approaching the preparation of water-soluble C 70 derivatives, we used a Prato reaction to provide fulleropyrrolidines, which we had reported for C 60 and M 3 N@I h -C 80 . 12,13 Unexpectedly, in the current C 70 Prato reaction, we found a new [5,6]-adduct, which was never observed in the previous C 70 Prato reactions reported.…”

“…Previous studies on cycloaddition of C 70 reported the generation of several monoadduct isomers. The Diels−Alder addition to C 70 formed [6,6]-adducts on ab-, cc-, and de-bonds, 3 while the [2 + 2] cycloaddition led to ab-, cc-, de- [6,6]-, and dd- [5,6]-adducts (see Figure 1a for the labeling of C 70 carbons). 4 The formation of the dd- [5,6]-adduct was also recently reported for the reaction of α,α′-dibromo-o-xylene to reductively activated C 70 5 and in the reaction with dichlorocarbene.…”

“…The Diels−Alder addition to C 70 formed [6,6]-adducts on ab-, cc-, and de-bonds, 3 while the [2 + 2] cycloaddition led to ab-, cc-, de- [6,6]-, and dd- [5,6]-adducts (see Figure 1a for the labeling of C 70 carbons). 4 The formation of the dd- [5,6]-adduct was also recently reported for the reaction of α,α′-dibromo-o-xylene to reductively activated C 70 5 and in the reaction with dichlorocarbene. 6 However, there is no report on [5,6]-monoadduct of C 70 by 1,3-dipolar cycloaddition.…”

Synthesis of a Dihydroxylated Open-Cage [70]Fullerene by a Reductive Ring-Closure Reaction

“…Due to a prolate spheroidal geometry, C 70 possesses four types of double bonds named with α, β, γ, and δ in which the strain energy decreases in this order (Figure ). Among them, the reactions at the γ- or δ-bond have been rarely observed since the hexagonal ring consisting of four γ-bonds and two δ-bonds is nearly planar and considered to adopt a benzenoid structure . Contrastingly, the most strained α- and β-bonds have the highest reactivities toward addition reactions .…”